In internal combustion engines, an encoder wheel can be used to determine the rotational speed of the internal combustion engine. A crankshaft angular range, referred to as a segment, can be assigned to a particular range of the piston movement of each cylinder of the internal combustion engine. These segments can be realized for example by markings on the encoder wheel coupled to the crankshaft.
A segment time in which the crankshaft passes through this angular range is a function of, inter alia, the energy converted in the combustion stroke. Combustion misfires, or other causes of uneven running of the internal combustion engine, are therefore reflected in the segment times. Accordingly, segment times are a measure of the uneven running of an internal combustion engine.
In order to make it possible to determine the uneven running from a segment time signal, the segment time signal must first be processed, and oscillations must be filtered out. For this purpose, an average segment time, or average value of the segment times, can be subtracted from the segment time signal. In DE 36 04 904, for example a floating average value is determined over two and eight segments of an encoder wheel. According to DE 43 19 677 A1, a cylinder-specific segment period duration is determined from the individual segment times using a weighted average value formation.
In this context the problem arises that the average segment time cannot be determined precisely, especially given comparatively large rotational speed gradients. Such large rotational speed gradients occur for example in coasting operation or freely falling operation of the internal combustion engine.
Therefore, it is desirable to provide a possibility for making it possible to determine the average segment time of an encoder wheel of an internal combustion engine in a simple manner.